In recent years, various electrophotographic photoreceptors having an amorphous silicon-based photoconductive layer have been proposed. Although an electrophotographic photoreceptor having such an amorphous silicon-based photoconductive layer has excellent mechanical strength, panchromatic property and sensitivity at the longer wave length it has disadvantages in that loss of image resolution increase when it is allowed to stand under high temperature and high humidity. Moreover, the surface is changed by friction with a residual toner-removing blade or a paper strip finger in the electrophotographic process, leading to the formation of white streaks (i.e., white lines) in the image obtained. In order to overcome the above problems, it has been proposed to provide a surface layer having such a composition, e.g., Si:N, Si:O, Si:C, that does not reduce the hardness of a silicon-based photo-conductive layer (for example, JP-A-59-147353, 59-165066, 60-112048, JP-B-62-12509). (The term "JP-A" as used herein means an "unexamined published Japanese patent application", and the term "JP-B-" as used herein means an "examined Japanese patent publication").
It is said that conventionally proposed electrophotographic photoreceptors having an amorphous silicon-based photoconductive layer decreases the formation of defects such as image deletion after repeated use, and has excellent electrophotographic characteristics. Furthermore, such an amorphous silicon-based photoconductive layer can produce a high quality image for a long period of time. Conventional electrophotographic photoreceptors, however, are either positively or alternatively negatively chargeable. An electrophotographic photoreceptor which is capable of being both positively and negatively charged is not known in the art.